import ee 
from ee_plugin import Map 

# Mark pixels where the elevation crosses 1000m value and compare
# that to pixels that are exactly equal to 1000m.

elev = ee.Image('CGIAR/SRTM90_V4')

# A zero-crossing is defined as any pixel where the right,
# bottom, or diagonal bottom-right pixel has the opposite sign.
image = elev.subtract(1000).zeroCrossing()

Map.setCenter(-121.68148, 37.50877, 13)
Map.addLayer(image, {'min': 0, 'max': 1, 'opacity': 0.5}, 'Crossing 1000m')

exact = elev.eq(1000)
Map.addLayer(exact.updateMask(exact), {'palette': 'red'}, 'Exactly 1000m')
